In electrophotographic image formation apparatuses (to be also simply referred to as “image formation apparatuses” hereinafter) which transfer a toner latent image on a transfer member to a printing sheet medium represented by normal paper and thermally fix the image to form a copy image, the desire to improve the image quality and productivity is growing more and more in recent years. To improve the productivity, the image formation velocity must be increased. More specifically, the driving velocity of movable members included in an image formation apparatus needs to be increased.
However, when the movable members are driven at a high velocity, vibration in driving or stopping them increases in geometric progression. The possibility of the vibration having an adverse effect on the image formation operation also increases.
Especially, when an exposure unit to electrostatically print electrostatic image information corresponding to image information uses laser irradiation by a polygon scanner, the irradiation accuracy of the laser beam on a charged unit such as a photosensitive drum is influenced by the above-described vibration of the movable members. For this reason, the vibration may directly result in uneven exposure accuracy and poor image quality.
If the movable members must inevitably be driven at a higher velocity to improve the productivity, the vibration generated by their operation will also unavoidably increase to some extent.
In a conventional image generation apparatus, to minimize uneven exposure accuracy by a vibration factor generated from movable members, the vibration property information (to be referred to as a “profile” hereinafter) of vibration generated by the operation of the movable members during image formation is measured and stored in advance. In actual image formation, vibration during image formation is predicted on the basis of the information. Exposure control to prevent any uneven exposure accuracy is executed, thereby limiting occurrence of uneven exposure accuracy.
The above-described prior art is disclosed in, e.g., Japanese Patent Laid-Open No. 58-121067.
In another method of minimizing uneven exposure accuracy by a vibration factor generated from movable members, image write by the laser is inhibited during the operation of moving the developing unit to prepare for development. However, if the need for a higher velocity grows, a problem may be posed in the productivity.
The above-described prior art is disclosed in, e.g., Japanese Patent Laid-Open No. 11-52661.
The vibration during image formation can be generated by various factors. More specifically, since the movement of the movable members changes depending on the operation sequence of image formation, it is not enough to use only one profile for all image formation operations.
In, e.g., a color image formation apparatus using a rotary developing unit, the rotation operation of the rotary developing unit for color switching is executed in parallel to the exposure operation for each color but in a different sequence. Hence, the profile also changes in each operation. Additionally, if vibration generated by the driving motor during the printing sheet medium convey operation which is executed simultaneously with image formation is to be taken into consideration, the profile may also change depending on the position of the paper feed cassette or the size of the printing sheet medium.
In such situations, the uneven exposure accuracy cannot be corrected by a single profile. Profiles corresponding to the respective situations must be prepared in advance.
The vibration property of a movable member can vary due to aging of the apparatus even in the same operation sequence. In this case, the vibration property of the movable members is not always the same because the state of the apparatus itself changes for a long term, although the change is not so large as that caused by the difference between the operation sequences.
For example, if the above-described rotary developing unit incorporates a toner bottle, the toner amount in the rotary developing unit always changes in accordance with the driving situation of the image formation apparatus. Since the weight of toner in the rotary developing unit constitutes a fair part of the total weight of the movable members, the change in toner weight has a nonnegligible effect on the rotation characteristic of the rotary developing unit. Hence, the rotation characteristic of the rotary developing unit varies even due to the remaining toner amount. In addition, the exposure operation does not always exhibit the same profile even when the rotary developing unit incorporates a toner bottle of the same color.
As a measure against this problem, profiles must be measured and stored in advance in various situations.
However, since the printing unit to store profiles has only a limited memory capacity, it is impossible to store profiles corresponding to all situations but only certain kinds of representative patterns can be stored. Hence, the uneven exposure accuracy cannot be corrected sufficiently because correction by the representative patterns has limitation.